Barry Murphy failed to make the semi-finals of the 50m freestyle at the London Olympics, while Melanie Nocher swam below par in 200m backstroke.
Murphy finished second in his heat in a time of 22.76, with the last placed qualifier, Eamon Sullivan of Australia, clocking a time of 22.27.
Talking to RTÉ Sport afterwards, he said: "I’m disappointed. I really felt like I could 22 low. I had been showing good speed and had already gone 22.7 this season. I thought if I could go a best time I would probably get a semi but it wasn’t to be today."
Murphy went on: "I felt like I got out of the blocks pretty well and I was moving well. I just tightened up a bit at the end. I tried to do with no breath and I think I paid the price.
"I was struggling for oxygen at the end. I’m pretty disappointed. I wanted to come here and swim my best and do my career best. I put a huge block of work in the last two years and I’m really disappointed it didn’t pay off.
"But this isn’t my last meet. I’m going to have plenty of more national and international meets so I must take the positives from what I did here."
He continued: "I really feel like I’m just coming into my prime now. Unfortunately in the Olympics they don’t have 50 strokes and the 50 breakstroke is by far my best event. I can do that at worlds and European level and hopefully do well.
"It’s a dream come true to be an Olympian. I just wish I had come here and performed to the best of my ability."
Melanie Nocher clocked a time of 2:16:29 that left her seventh in her heat - well back on the 2:10.75 she set at this year's European championship.
Nocher was clearly distressed after the race and subsequently revealed that she has been suffering with gastrointensitis.
On her twitter account @MelanieNocher, she said: "Well I gave it my best - have had gastrointensitis since Sunday so have been feeling anything but good. Least I can say I gave it my all."